Motor control circuit



June 2, 1953 I w. J. BROWN 2,640,959

MOTOR CONTROL CIRCUIT Filed July 8, 1950 5 Sheets-Sheet 2 5| ALTERNAT- ALTERNATING me VOLTAGE VOLTAGE SOURCE 1 solg acz DIR'EGT CURRENT I I SOURCE' as? I PHASE LEJ lRAgE RESPONSIVE SOURCE L ELECTRIC PWER I CONVERTE F 90 94 53 o SECOND TYPE PHASE VOLTAGE SHIFTING SOURCE NETWORK 99 a2 CONTROL VOLTAGE LOAD SUPPLY wk 95 INVENTOR.

WALTER J. BROWN 5 Sheets-Sheet 5 W. J. BROWN MOTOR CONTROL CIRCUIT INVENTOR.

.[Lr w i l WALTER J. BROWN June 2, 1953 Filed July 8, 1950 June 2, 1953 W. J. BROWN MOTOR CONTROL CIRCUIT 5 Sheets-Sheet 4 Filed July 8, 1950 INVENTOR.

w womzom L #5550 SE5 7 BY WALTER J. BROWN kW/mm.

June 2, 1953 r w. J. BROWN 2,640,959

MOTOR CONTROL CIRCUIT Filed July 8, 1950 5 Sheets-Sheet 5 l0 3 23| 222 2%5 I 220 223 224 22s 23:

Fig. l5

IN V EN TOR.

WALTER J. BROWN Patented June 2, 1953 UNITED STATES PATENT OFFICE My invention relates in general to control systems and especially to electrical control systems in conjunction with space discharge devices.

This application is a continuation-impart of my application Ser. Nos. 770,968, 770,966 and 770,967, all of which were filed August 28, 1947, and entitled, respectively, Phase Shift System, Phase Shift Network and Phase Shift Bridge, and of my application Ser. No. 779,909, filed October 15, 1947, and entitled Phase Shift Circuit, now Patents Nos. 2,524,761; 2,524,759; 2,524,760 and 2,524,762, respectively, all of which were issued on October 10, 1950.

An object of the invention is to provide a sensitive control of a space dis-charge device to control the conversion of energy from one form of electrical energy into another form.

Another object of the invention is to provide a sensitive phase shift system to control a space discharge device such as a gaseous rectifier, thus controlling the conversion of energy between alternating and direct current systems.

Another object of my invention is a phase shifting system for a rigid controlled rectifier supplying rectified current to a direct current motor.

Another object of my invention is the provision of a phase shifting network as applied to an electrical motor operable from a rectified alternating voltage source, wherein the phase shifting network is responsive to electrical changes in the motor operation and consequently shifts the phase of the grid of the rectifier tubes in accordance thereto.

Another object of my invention is the combination of an electric motor operable from thermionic rectifiers and a phase shifting network of high sensitivity capable of shifting the phase of the grid of these thermionic rectifiers more than 180 degrees relative to the energizing voltage of the phase shifting network, and which retains its high sensitivity over a full 180 degree phase shift.

Another object of my invention is a sensitive phase shifting network for use with a phase responsive electric power converter which network is controlled by the same type voltage as utilized in the load of the converter.

Another object of the invention is to provide a phase shift network to control a controllable rectifier supplying rectified current to a motor wherein the phase shift network and the rectifier are energized with voltages from either a single phase source or from different phases of an alternating current source such that in the event of failure of a variable reactance tube in the phase shift network the output voltage of the phase shift network will shift in phase in a direction to reduce the speed of the motor.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims, taken in conjunction with th accompanying drawings, in which:

Figure 1 is a circuit diagram of a sensitive phase shifting system which may be used in my energy conversion system;

Figure 2 is a voltage vector diagram depicting the voltage vectors obtainable from the circuit of Figure 1;

Figure 3 is a modified phase shift system that may be used in conjunction with my energy conversion system;

Figure 4 is a voltage vector diagram depicting the voltage vectors obtainable from the circuit of Figure 3;

Figure 5 is a still further modification of a phase shift system that may be used with my energy conversion system;

Figure 6 is a voltage vector diagram of the vectors obtainable from the circuit of Figure 5;

Figure 7 is a still further form of phase shift system for use in my energy conversion system;

Figure 8 is a voltage vector diagram of the vectors obtainable from the circuit of Figure 7;

Figure 9 is a block diagram of an electrical system utilizing my phase shifting network for control of a phase responsive electric power converter;

Figure 10 is a circuit diagram of a motor control circuit having a phase shifting based on Figure 1 with a quadrature feedback circuit therein and embodying the principles of my invention;

Figure 11 is a circuit diagram of an alternative arrangement of a quadrature feedback circuit as used in the circuit of Figure 8;

Figure 12 is a circuit diagram of a direct current motor system which includes the embodiment of my phase shifting system of Figure 5 to control a grid controlled rectifier for the said direct current motor;

Figure 13 is a circuit diagram of a direct current motor system which includes the embodiment of my phase shifting system of Figure 7 to control a grid controlled rectifier for the said direct current motor;

Figure 14 is a circuit diagram of a motor control system for motor armature energization from a, rectifier controlled by a phase shift system of Figure 3;

Figure 15 is a circuit diagram of a modification of the circuit of Figure 14 for generator field control; and

Figure 16 is a circuit diagram of a motor control system for motor field energization from a rectifier controlled by a phase shift system of Figure 3.

My energy conversion system has as its basis a sensitive phase shift system to control the energy passed by a space discharge device such as a controllable gaseous rectifier. My converter may be defined as comprising one or more space discharge devices provided with control means. The space discharge devices may comprise vapor or gas-filled rectifier tubes with thermionic cathodes or with pool type cathodes, such as mercury arc rectifiers. The control means may comprise an internal or external electrode or magnetic field. The circuit of Figure 1 shows a sensitive phase shift system wherein 2i designates an alternating current or periodic voltage source having first and second terminals 22 and 23. Serially connected across the first and second terminals are first and second impedances 24 and 25. The impedances 24 and 25 has a junction 26 and serially connected across the impedance 25, namely, at the junction 26 and the terminal 23, are first and second reactances 21 and 28 which comprise a second branch circuit 31'. A first output terminal is connected to the first terminal 22 and a second output terminal P is connected at the junction of the first and second reactances 21 and 28. These reactances have been shown as being mutually variable by an arrow therethrough, and it is to be understood that either or both of these reactances are variable as long as the relative impedance of the elements in this branch circuit is achieved. The first and second reactance elements 2! and 28 are of opposite reactive sign.

The first and second impedances 24 and 25 have been designated 1 and 52 to designate that the phase angles of these impedances are diiferent. In this phase shift system the phase angles are preferably at quadrature relationship.

The vector diagram of Figure 2 may be referred to as an aid in understanding the operation of the circuit in Figure 1. The voltage of the alternating current source 2| has been designated E21 and extends horizontally to the right as a reference voltage. The potential at the terminals 22 and 23 has been designated by the points 22' and 23. Similarly the potential at the terminal 26 has been designated by the point 26. The voltages across the impedances 24 and 25 have been designated by the voltage vectors E24 and E25, and likewise the voltages across the reactances 21' and 28 have been designated E27 and E22. An output voltage of the phase shift system appears between the terminals 0 and P, and hence the points 0 and P designate the ends of the output voltage vector Emit.

Upon varying the relative impedances of the reactive elements 21 and 28, the relative lengths of the vectors E27 and E23 will vary, thus to shift the potential of the output terminal P. The point P will follow a locus such as designated by the are 29 on the vector diagram of Figure 2. By keeping the Q of the reactances 21 and 28 constant as the relative impedance is varied the locus 29 may be made the arc of a circle having the baseline E25 as a chord. This may readily be seen from geometric theory. From the voltage vector diagram of Figure 2 it will be observed that the point 0 has been placed at the approximate center of the arc. Thus as the relative impedance of the reactive elements 21 and 28 is varied the point P will travel about the arcuate locus 29, thus to shift the phase of the output voltage E011: relative to the alternating current input voltage E21.

The impedances 24 and 25 have been stated as having phase angles substantially at quadrature which makes the angle between the voltage vectors E24 and E25 substantially a right angle. With the input voltage vector E21 extending to the right the impedances 24 and 25 could be a resistance and an inductance, respectively, or they could be a capacitance and a resistance, respectively. If the impedances 24 and 25 were made a resistance and a capacitance, respectively, or an inductance and a resistance, respectively, then the point 26 would be above the horizontal input voltage vector E21. This Would necessarily make the chord E25 above this input voltage vector E21. If constant magnitude of output voltage is not essential, but merely a large angle of phase shift desirable, then particular care need not be taken to establish the point 0 at the center of the arcuate locus 29 and also particular care need not be taken to maintain a substantially constant Q in the variable element.

The circuit diagram of Figure 3 is a modification of my phase shift system wherein the alternating current source 2| energizes serially connected impedances 3i and 31 having substantially the same phase an le, designated as 21. The first output terminal 0 is connected at the junction of these impedances 30 and 3|, and these impedances form a first branch circuit 32.

A third branch circuit 33 is also connected across the alternating current source 2| and includes a fifth impedance 36 and, also includes impedance means 28 which consists of a third impedance 34, and a fourth impedance 35. The fourth and fifth impedances 35 and 35 have similar phase angles designated as 2 and the third impedance 34 has another phase angle designated as 23. The third and fourth impedances 34 and 2: may be lumped together as impedance means A second branch circuit 3'. is connected across the fifth impedance 3G and it includes the first and second reactances 2i and 28. The second output terminal P is connected at th juncture of these reactances.

The vector diagram of Figure 4 shows the vectors obtainable from the circuit of Figure 3 with vectors designated in a fashion similar to those in the vector diagram of Figure 2. The vectors E30 and E31 show that the first and second impedances 3B and 3i have phase angles 1 which are substantially the same. The impedanc means 38 has a voltage vector E33 which is the combination of the phase angles (22 and 3 of the impedances 35 and 34, respectively. The phase angle 52 of the impedances 35 and 36 may be the same as the phase angle 1 of the impedances 30 and 3!; however, this phase angle 2 should be substantially at quadrature with the phase angle 3 in order to place the baseline E36 in a position such that the potential of the point 0 lies substantially at the center of the arcuate locus 29. The impedance means 28 may, however, preferably consist of a single impedance element having a phase angle such as shown by the vector E32 and its phase angle may be in quadrature with 2 of impedance 36 so that the angle between the vectors E32 and E36 is a right angle. Similarly the phase angles of impedances 30 and 31 are preferably identical so that E30 and E31 are collinear and equal, so that they form a diameter of the are 29, assuming said are to be circular. In fact, the two impedances 3i] and 3| may be two equal portions of a transformer winding which supplies energy to the phase shifting network.

The circuit diagram of Figure 5 shows a still further modification of my phase shift system which includes a first branch circuit 39 connected across the alternating current source 2|. This first branch circuit 39 includes serially connected first, second and third impedances 49, 4| and 42. A third branch circuit 43 is also connected across the alternating current source 2| and includes fourth and fifth impedances 44 and 45 serially connected with the first output terminal connected therebetween. These fourth and fifth impedances 44 and 45 have been shown with phase angles 1 and c2, respectively, and these phase angles are preferably substantially at quadrature. The second branch circuit 31 is connected across the second impedance 4| and this second branch circuit 31' incdludes the reactances 21 and 28 with the second output terminal connected therebetween.

The vector diagram shown in Figure 6 is an explanation of the vectors obtainable from the circuit diagram of Figure 5 with the vectors thereon indicated in a fashion similar to the vector diagrams of Figures 2 and 4. It will be noted that the vectors of the impedances 40, 4| and 42 as depicted in Figure 6 do not lie on a straight line, rather, the baseline vector E41 is at a considerable angle to the input voltage vector E21. This is so that the baseline vector E41 will, with the first output terminal 0, form an isosceles triangle having the baseline vector E41 as a base. The vectors E44. and E45 show that the phase angles in and I 2 of the impedances 44 and 45, respectively, are substantially in quadrature. However, the vectors E40, E41 and E42 are preferably established by a single impedance means 39 having tappings at each end of impedance 4| and in this case the vectors E40, E41, and E42 are collinear. This single impedance means 39 may conveniently comprise a winding of a transformer which also comprises the phase shifter and which is divided by tappings into three sections 49, 4| and 42.

The circuit diagram of Figure '7 shows a still further modification of a phase shift system which may be used with my energy conversion system, and this circuit includes the second branch circuit 31 as before which includes the first and second reactances 21 and 28 with the second output terminal P connected therebetween. Also connected across the alternating current source 2| is a first branch circuit 46 which includes third and fourth reactances 41 and 48 having the first output terminal 0 connected therebetween.

The Figure 8 is a vector diagram of the vectors obtainable from the circuit of Figure '7 with these vectors designated in a fashion similar to that shown in the vector diagrams of Figures 2, 4 and 6. In this case the voltage vector of the alternating current source 2| is also the baseline vector across which the variable reactances 2'! and 28 are serially connected. In the circuit of Figure '7 the Q of the first branch circuit 46 has been made approximately half the Q of the third branch circuit 31 in order that the potential of the first output terminal 0, designated by the point 0, will be at or near the center of the arcuate locus 29. There is another method for establishing the point 0 at or near the center of the arcuate locus 29. The energizing voltages for each of the branch circuits 3'! and 46 may be unequal, and in such event, the product of the Q of branch circuit 31 times the energizing voltage of this branch circuit should be substantially twice the product of the Q of branch circuit 46 times the energizing voltage of this branch circuit.

In all the circuits of Figure 1, Figure 3, Figure 5 and Figure 7, the first and second reactive elements 2! and 28 must necessarily be of opposite sign to span the baseline chord of the locus 29 with point P removed a considerable distance therefrom. Previously, it has been stated that the Q of the second branch circuit 31 is maintained substantially constant as the relative impedance of the elements therein is varied. This may be accomplished by selection of the proper type of reactive elements and one form of reactive element which will accomplish this purpose is the use of a reactance tube. The preferred form of a reactance tube comprises a pentode having a very high internal plate resistance such that the plate current is substantially independent of the plate voltage. The pentode is operated at constant screen voltage and an alternating current feedback circuit is provided from plate to grid so as to establish an alternating current grid-cathode voltage which is substantially in quadrature with the alternating current plate-cathode voltage, and which is superimposed on a direct current negative grid-biasing voltage. The alternating current plate current is in phase with the alternating current gridcathode voltage and is accordingly substantially in quadrature with the alternating current plate-cathode voltage. Accordingly the tube exhibits the properties of a reactance having a Q which is dependent upon how nearly the phase angle of the alternating current feedback circuit approximates degrees. Another approach to the explanation of how the are 29 may be substantially circular is to state that the phase angle between vectors E21 and E28 is substantially constant. For the phase shifting network of Figure 7, it will be seen that the first output terminal 0 can be established at the center of such a circular are if the point O and vector E21 establish an isosceles triangle with vector E21 as a base and if the phase angle between the vectors E41 and E48 is substantially twice the phase angle between the vectors E27 and E28- Figure 9 illustrates in block form the adaptation of my phase shifting network to an electrical system that converts a first type of voltage into a second type of voltage for utilization in a load. A first type voltage source 90 supplies a first type voltage to a phase responsive electric power converter 9| and to a phase shifting network 53. The phase responsive electric power converter 9| converts the first type of voltage of the first type voltage source 90 into a second type of Voltage for utilization in the load 92. A control voltage supply 93 obtains or generates a second type of voltage from, or in accordance with the operating conditions of, the load 92, for controlling the phase shifting network 53. A second type voltage source 94 supplies a second type voltage for the phase shifting network 53. The first and second types of voltages may be an alternating current voltage and a direct current voltage, or vice versa. One or the other of the first and second type voltage sources will be an alternating or periodic voltage source, and the phase shifting network 53 is capable of shifting the output voltage across the terminals 0 and .;.mo. u e adi t n m e ,rnodulated carrier wave to the load .92,'which electric power converter -9i. voltage source 94 would hea direct current VOltage source supplying operatin Voltages ,to the ;-phase shifting network -53. {The direct current :voltage obtained from the rectifier device 9| would Ice-controlled in accordance withthe-oper- VP thereof relative to a ;reference voltage of alternating voltage source. In operation, the

electrical system as depicted in the Figure 9 maybe applied in analogy to a frequency modu lated radio transmitter, a where the first type voltage source 90 supplies a direct current voltage to both the phase shifting network 53,

which would be the phase modulator, and to the phase responsive electric power converter 8],

which would be the frequency multiplier and/ or amplifier circuit v of the rest of the frequency The phase -responsi-veeleotric power converter 9| would supply an alternating'lvoltage in theform of a frequency wopldgbe-an antenna or other similar load. The

control voltage-supply 93 would be an alternating voltage in the form of modulation energy, and as represented by, the dotted lines 95 would be in accordance with the modulation requirement needed by the-load, to supply modulation voltage to the phase shifting network '53.

It will be seen that the control voltage is of the second type of voltage, namely, an alternating voltage.

Thesecond type voltage-source 94 would be the carrier wave input energy which the-modulation voltage of the control-voltage source 93 modulates.

It w,ill beseen that :the electrical system of the HFigureQ, as pertaining to a frequency modulated radio transmittenconverts direct-current or constant voltage ;;power into an alternating voltage power for-utilizationin the load.

'The electrical system of Figure 9 may also be used to depict-the circuit operation of themotor control circuit .wherein a direct current motor is operated -from a rectified alternating voltage u n hi an o y, th fi pe o t source :90 would be an alternating voltage source supplying both the phase shifting network 53 and the phase esponsive electric power converter 9| which ;would be a rectifier device. lfihe phase responsive electric power eonv erterfl l or rectifier device, supplies rectified alternating voltages to a load 92 which wouldbe a direct current motor, or other load utilizing a direct current voltage. The control voltage supply 93 w u ut l th seco p vo tage obtain d from, or in accordance with, the load v92, to ans th hp rat s ondit o of the p as shifting network;53, in order that the phase shifting ne twork maycontrol the phase responsive The second type ,ating conditicnsof the load orinotor 92 through the medium of the;control voltage supply 93 and the phase shifting network 53. This could be accomplishedgby,havinga reactance tube in the phase shifting network which is controlled by the direct current voltage of the control voltage supply-393 to vary the bias of this reactance tube, and consequently its eiiective reactance or impedance. Thisvarying impedance of the reactance tube in the phase shifting network 53 can be made to .varythe operating conditions of the phase shifting network 53, and'consequently-the phase of the output voltage across the terminals O and P-relative to the phase of the alternating :..voltage obtained from the first type voltage sourceBU.

'The Figure :10 illustrates an application of, a

8 -form of my phase shifting network of Figure l as applied to a motor control circuit or other device requiring a rectified alternating Voltage input. An alternating voltage source 5| supplies voltage to a rectifier device 52 and to a phase .shif-tingnetwork153. The rectifier device .52 supplies -rectified alternating voltage to a load or motor armature 56. A controlled voltage source 80, which is responsive to operating conditions of the -load or motor -56, is connected to the phase shifting network 53 for controlling same. A direct current source159 supplies a constant direct voltage to the phase shifting network 53, which in turn supplies -a voltage variable in phase relative to the alternating voltage source 51 for controllingthe rectifier device 52. A field winding 10 is also connected across the direct current source, 59. The rectifier device 52 has space discharge devices for rectification, which for purposesof ;i llust ration,;but not limitation, have been shown as rectifier tubes 54 and 55, to supply full wave rectifiedcurrents to the load which is illustrated as a direct current motor armature 56. Th spacedischare d i 01;TeCtifiel ube 54 and 55 haveisome form ,of control means, illustratedby grids and 58, respectively, connected to;a grid transformer 59. The phase shiftin -network 53 has first and second-input terminals -A and B, respectively, connected across the alternating voltage source 15!, and first andsecond 01. tha ;t rm ha an s i e s pp yin the gridtransiorrnenfis. The phase shifting network 53 includes a resistance 50, an inductive winding 61, a-eapacitance ,52, and a variable in- ;ductance 63. '1jheresistance 6 0 and a portion of tl1e;inductive windin 6 I are connected acrossthe input terminals A and B, and the capacitance 52 and variable inductanceflvare serially connected across the inductive winding 61 with the second thereon. Th phase Shifting network-53 has first an secon contro termi l X h connected t t c nt olle :rol aeesou fq fifi wi t r control terminal 2; being oonnected-to the Junetiqno th s ti t mihal th motor arm tur -5 ah i-aneehd-o th s un r i a 68, dthe s con con r -termina Ybei e o e ed to th p l on h s u r s a 68 through a filter resistor 85. Within the phase sh tft anetwq t r o t o rm na X .i c rm edt the oh rc grid 14 hrou a s n lfilah .th a hq l th q sh a o denser H. The second control terminal Y is connected to the; controlling voltage potentiometer thr an. e era io l miti re o 18 and aispee ant al-p ent om te l enam e a ionil mi n ondense 0n e th ;a celera onrrssi 1' d a o t o o the :potehtiome erlfi torre t ther wi m delay c rcui Bh a adra u f a circu :81 i

;cludes aresistance v55 andarcondenser 6 6,,which retards the 1 phase of the voltage applied to the 99 1, 59 su flfle 'ihe lll t 64 wi act as an induc an 1 qe de e ifli connec in zr e Mimi-insistenc 6 i zthe arqu i' twen g the anode I2 and the control grid I4, in order to isolate these two elements of the tube 64 for direct current voltages. The condenser 84 and the resistance 10 tend to destroy the quadrature feedback effect of the quadrature feedback circuit 8 I. To counteract the advancing of phase as produced by the condenser 04 and the resistance I6, I show a modified quadrature feedback circuit 8| in Figure 11. The modified quadrature feedback circuit 8 I includes the resistance 65 and the condenser 66 as before, but also includes a further resistance 82 and condenser 83 to further retard the phase, in order to obtain a feedback voltage to the control grid I4 that is as close to 90 degrees retarded as desired.

In the rectifier device 52, a self-biasing means 86 is provided to help prevent accidental firing of the tubes 54 and 55 on the negative half cycle. Grid loading means 81 are connected in the gridcathode circuit of the tubes 54 and 55 to prevent an effectual short circuit of half of the grid transformer when the respective tube is firing.

In operation, the alternating voltage source 5I supplies an alternating voltage of fixed magnitude and phase to both the rectifier device 52 and the phase shifting network 53. The phase shifting net work 53, being responsive to the controlled voltage source 80, controls the rectifier device 52 by supplying a phase shifted voltage from its output terminals and P. The voltage vector diagram of Figure 2 generally represents the voltage vectors obtainable from the phase shifting network 53, wherein the variable inductance 63, which is a reactance tube, varies the potential at the output terminal P about a circular locus, with the point 0 at the center thereof. The settings of the speed control potentiometer I9, and the acceleration limiting resistor I8 govern, respectively, the ultimate speed of the motor 56, and the rate of acceleration in coming up to that speed. The controlling voltage source 61 in opposition to the controlled voltage source 80 determines the bias at which the thermionic tube 64 operates, thereby determining its impedance, and consequently the operating point on the arcuate locus of the voltage vector diagram. When there is a high negative bias, the tube 64 has a high impedance, and the position of the point P" on the voltage vector diagram will be at its furthermost clockwise position. In this position, the voltage across the terminals 0 and P is 180 degrees out of phase with respect to the phase of the voltage of the alternating voltage source I, and thereby the rectifier device 52 has no output. This provides a measure of safety should the tube 64 fail, for then the impedance thereacross would be infinite, and the rectifier device 52 would reduce its output to zero. When there is a low negative bias condition of the tube 64, the impedance of the tube 64 is low, thereby shifting the operating position of the point P in a counterclockwise direction. The point P" may easily be shifted counterclockwise to permit the output voltage across the terminals 0 and P to be directly in phase with the voltage of the alternating voltage 5I, thereby allowing the rectifier device 52 to have a full output. The speed control potentiometer I9 governs the. speed of the motor armature 56 between these two limits, and consequently is connected across only a portion of the controlling voltage source 61 to establish these limits of control. The controlled voltage source 80 obtains a voltage that is proportional to speed from the shunt resistance 68. The control terminal X, which is connected to the shunt resistance, applies to the grid I4 a negative voltage approximately proportional to speed, which, as the speed increases, increases the negative bias of the tube 64 and consequently the impedance thereof, to decrease the output of the rectifier device 52 to maintain the speed substantially constant. The control terminal Y furnishes a return path for the direct current voltages obtained from the controlled voltage source through the opposing controlling voltage source 61. The voltage obtained from the control led voltage source 80 will not be a pure direct current, inasmuch as the motor 56 is being supplied with pulses of current from the rectifier device 52. A filtering arrangement for the controlled voltage is furnished by the condenser TI and the filter resistor 85. A further filtering action is obtained by the resistance I6 in conjunction with the condensers 84 and 66. This filtering action assures that direct current control voltages are applied to the biasing means 61.

Figure 12 illustrates my phase shifting system as used in conjunction with a three phase power supply and a grid controlled rectifier for supplying rectified power to a direct current motor. The system includes generally, a direct current motor armature I04, a grid controlled rectifier system I03 for supplying rectified power to the motor I04, a phase shifting system I02 for controlling the grid controlled rectifier system I03, a direct current source I I I for supplying operating voltages to: the phase shifting system I02, a controlled voltage source I I2 for controlling the operating conditions of the phase shifting system I 02, and a three phase supply source IOI for supplying alternating voltages to the phase shifting system I02 and to the grid controlled rectifier I system I03. The phase shifting system I02 includes three phase shifters designated I05, I06 and I01, respectively. The grid controlled rectifier system I03 includes rectifiers I 08, I09 and I I0, respectively. The three phase supply source IOI has three phases C, D and E, with the phase shifters I05, I06 and I01 energized, respectively, from the phases 0, D and E. The rectifiers I08, I03 and IIO are energized, respectively, from the phases D, E and C. It will be seen that the rectifier I08 is energized from a different phase than the phase that is energizing the phase shifter I05. This has been done purposely as a safety measure which will be discussed more fully later. The motor control system is operable with only the phase shifter I05 and the rectifier I08, omitting the phase shifters I06 and I0! and the rectifiers I09 and I I0. For this reason, the latter two phase shifters and rectifiers have been shown as having switches I39 to I44, for disconnection from thesupply voltages and the load, which is to illustrate that the motor control system is operative either with or without these elements as part of the motor control system. The motor control system may be fully described by describing only the phase shifter I05 and rectifier I08, which will describe the operation of only single phase power supplied to the motor I04. It will be readily apparent to those skilled in the art that such a system for one phase may be easily duplicated for a three phase system or any polyphase system.

The phase shifter I05 is of the type of phase shifting system as shown in Figure 5, and vectorially illustrated in Figure 6. An input transformer H3, which is connected across phase C, has two taps H4 and H5 on the secondary IIB thereof. A resistance or resistive element H6 and a. capacitance or capacitive element III are serially connected across the ends of the secondary I IS, with the first output erm'mn O of the phase shifter connected therebetween. A capacitance or capacitive element II 9 and a' variable quadrature feedback circuit to make the therm ionic tube I2I exhibit the properties of a re actance tube, or in this case specifically as an in duct an ce. The thermionic tube I2I has a plate I24, a screen grid I25, a control grid I26 a c'athf ode I 21 and a suppressor grid I45 connctedto the cathode I27. Biasing and high voltage supplies are supplied to the tube I2I by a voltage divider I28 connected across the terminals of the direct current source III. Eositive direct current potentials are applied to the screen I25 and plate I24, and a nega-tivepotential is applied to the cathode I27. A voltageregulator' tube I29 is connected across the plateand screen supply voltages. The operation of the phase shifter I05 is similar in operation to the operation of the circuit of Figure 5, wherein the potential of the output terminal 1? is variable throughout an arcuate locus by varying the variable inductance I20.

The rectifier I08 islillustrative of connection to one leg i3 I cf a. delta-star connected three phase transformer, The secondaryof theleg I3I has a rectifier tube I32 and themotorarmature I04 connected acrossit. Theoutput of the rectifier tube I32 is supplied to the motor armature I by the aforementioned series connection. The rectifier tube I32 has a plate I33, a grid I34 and a cathode I35. The output of the phase shifter I is supplied through an output transformer I30 to the grid I34 with respect to the cathode I35 of the rectifier tube I32 The star point, illustrated at one end of the secondary of the transformer leg I 3 I would be the star point or common point of the secondary of a three phase trans-"' former, if a three phase rectifier system were used.

The controlled voltage source I I2 includes a shunt resistance I36 connected across the motor armature I04. The shuntresistance I36 has a tap connection I31 for supplying a direct current feedback voltage to the phase shifter I05 through a movable contact I38 on thevoltage'dividerllgti. The direct current feedback voltage obtained from the shunt resistance I36 supp1ie'sa negative voltage to the grid I26 of the tube ljl, whereas the voltage divider I28 supplies eithera negative or a positive controlling voltage control the amount of resultant bias applied to the tube I2 I. The amount of biassupplied to the tube I2 I determines th eflective reactance of this tube, and consequently the operating position of the output terminal Pon the arcuate locus of the voltage vector diagram.

In operation, the three phase supply source I01 supplies alternating voltages of fixd'ma'g'nb' tude and phase relationships to both the rectifier I08 and the phase shifter I05. Thephase' shifter I05 being responsive to the controlled voltage source H2 andtlre controlling voltage source I28, controls the rectifier I08 ljy siippl'ying a phase shifted voltage from its output terminals 0 and P. The voltage vector diagram of Figure 6 represents the voltage vectors obtainable from the phase shifter I 05, wherein the variable inductance I20, which is a reactance tube, varies the potential at the output terminal P about an arcuate locus, with the point 0 at or near the center thereof. However, the vectors E40, E41 and E42 are collinear rather than angularly related as shownin Figure 6. The setting of the movable contact I38 governs the ultimate speed of the motor armature I04. The combination of the direct current feedback from the shunt resistor I30 and the controlling voltage obtained from the voltage divider, I28, determines the bias applied to the tube I2 I. This bias determines the effective reactance of the tube I2I, and consequently the operating point on th'e'arcuate locus of the voltage vector diagram. When there is a high negative bias the tube IZ I has a high impedance or high efiectivereactance, and the position of point P will be' at its furth ermost clockwise position. In this position, the voltage vector Eollt on the vector diagram of Figure 6 is about 60 degrees lagging of a zeroreferenc'e line. The input voltage I I5II4 obtained across the secondary of the input transformer I23 will be considered as the reference voltagehaving a zero phase according to standard electrical practice, or in other words the vector of the voltage I I5I I4 will be horizontal to the right. This vector represents the phase C, and, as will be seen at the upper right of the Figure 12, the'vector representation issuch that the phase D leads the phase C by degrees. This'means that the phase of the voltage applied to the rectifier I08 is 120 degrees leading with respect to the phase of the voltage supplying the'phase shifter I05. Under a condition of high negative bias, with high effective reactanceof the inductance I20, the vector 0-? will be 60 degrees lagging the reference voltage I I5II4; and the voltage applied across the plate I33'and cathode I35 of the rectifier tube I32 is 120 degrees leading this reference voltage. Therefore, it'will be'seen that the voltage applied to the grid I34 will be degrees lagging the plate-cathode voltage. Under this condition, the tube will'not fire during any portion of the cycle. This is the'measure of safety which was recited earlier, in that should the tube I2I fail for any reason; which means it would have a theoretically infinite impedance, the phase of the voltage across the terminals 0 and P of this phase shifter I05 would then be such as to cause the rectifier I08 to be turned off. This measure of safety is quite importantto prevent the motor armature I04 from going to a high or full speed from its former predetermined speed setting upon the failure of the reactance'tube I2 I. Care must be taken in the circuit design to prevent more than 180 degrees lagging current, or this will cause this rectifier tube to turn full on, with full excitation supplied to the motor armature I03. A fixed phase shifting network may be supplied in the circuit in such a manner to prevent such an occurrence, and I have found that the output, transformer I30 and the resistancecapacity filters in the grid circuits of the rectifier tubes cause a slight shift in phase which also must be taken into account in the design of the circuit.

When there isa low negative bias condition applied to the tube I2I, the impedance or effective reactance of this tube I2I is low, thereby shifting the operating point of the output terminal P in acounterclockwise direction. The point P on the voltage vector diagram may easily be shifted counterclockwise sufliciently to permit the output voltage across the terminals 0 and P to be directly in phase with the voltage applied to the plate and cathode of the rectifier tube I32. This allows the rectifier tube I32 to have a full output. The controlled voltage source II2 obtains a voltage that is approximately proportional to speed from the shunt resistor I36. As the speed of the motor armature I04 increases, a greater voltage is obtained across the shunt resistor I36, thereby applying a more negative voltage to the grid I26 of the thermionic tube I2I, which increases its effective reactance and thereby causes the output voltage O-P to be more lagging to reduce the output of the rectifier I 08 and consequently lower the speed of the motor armature I04. Thus a balance is always maintained between the controlled voltage taken from the motor armature I04 and the controlling voltage applied from the biasing voltage divider I28; thus, the motor voltage is held substantially constant at a value dependent upon the setting of the controlling voltage divider I28.

The operation of the phase shifter I 05 and rectifier I08 are complete as they have been described as being excited from different phases of a three phase supply. As mentioned above, other phase shifters I06 and I01 may be employed in conjunction with other rectifiers I09 and I I0, by closing the switches I39, I40, I43 and I44. Switch means MI is shown for connecting the direct current source III and the control voltage supply II2 to the phase shifters I06 and I01, and switch means I42 is also shown for connecting the output of the reotifiers I09 and III] to the motor armature I04. Alternatively, when only a single phase supply is available, the phase shifter I05 may be energized from the same phase as the rectifier I08, through a fixed phase shifting network which will displace the output voltage of the phase shifter so that the grid voltage of the rectifier can never lag by more than 180 degrees behind the voltage applied to the plate of the rectifier.

Figure 13 illustrates my phase shifting bridge of Figure 7 as used in conjunction with a three phase power supply and a grid controlled rectifier for supplying rectified power to a direct current motor. The system includes generally, a direct current motor armature I54, a grid controlled rectifier system I53 for supplying rectified power to the motor armature I54, a phase shifting system I52 for controlling the grid controlled rectifier system I53, a direct current source I6I for supplying operating voltages to the phase shifting system I52, a controlled voltage source I62 for controlling the operating conditions of the phase shifting system I52, and a three phase supply source I5I for supplying alternating voltages to the phase shifting system I52 and to the grid controlled rectifier system I53. The phase shifting system I52 includes three phase shifters designated I55, I56 and I51, respectively. The grid controlled rectifier system I53 includes rectifiers I58, I59 and I60, respectively. The three phase supply source I5I has three phases C, D and E, with the phase shifters I55, I56 and I51 energized, respectively, from the phases 0, D and E. The rectifiers I58, I59 and I60 are energized, respectively, from phases D, E and C. It will be seen that the rectifier I58 is energized from a different phase than the phase that is energizing the phase shifter I55. This has been done purposely as a safety measure, similar to that explained for the circuit of Figure 12. The motor control system of Figure 13 is operable with only the phase shifter I55 and the rectifier I58, omitting the phase shifters I56 and I51 and the recti-' 14 fiers I59 and I60. For this reason, the latter two phase shifters and rectifiers have been shown as having switches I89 to I94, for disconnection from the supply voltages and the load, which is to illustrate that the motor control system is onerable either with or without these elements as part of the motor control system. The motor control system may be fully described by describing only the phase shifter I55 and rectifier I58, which will describe the operation of only single phase power supplied to the motor armature I54.

The phase shifter I55 is of the type of phase shifting bridge as shown in the Figure 7, and vectorially illustrated in Figure 8. An input transformer I63, which is connected across phase 0, has end terminals I64 and I65 on the secondary I68 thereof. A capacitance or capacitive element I66 and an inductance or inductive element I61 are serially connected across the ends I64 and I65 of the secondary I68, with the first output terminal 0 of the phase shifter connected therebetween. A capacitance or capacitive element I69 and a variable inductance or inductive element I10 are serially connected across the end terminals I64 and I65 with the second output terminal P of the phase shifter connected therebetween. The variable inductance I10 includes a thermionic tube HI, and a resistance I12 and capacitance I13 forming a quadrature feedback circuit to make the thermionic tube I1I exhibit the properties of a reactance tube, or in this case specifically as an inductance. The thermionic tube I1I has a plate I14, a screen grid I15, a control grid I16, and a cathode I11. Biasing and high voltage supplies are supplied to the tube IT! by a voltage divider I 18 connected across the terminals of the direct current source I 6I. Positive direct current potentials are applied to the screen I15 and plate I14, and a negative potential is applied to the cathode I11. A voltage regulator tube I19 is connected across the plate and screen supply voltages. The operation of the phase shifter I55 is similar in operation to the operation of the circuit of Figure 7, wherein the potential of the output terminal P is variable throughout an arcuate locus by varying the variable inductance I10.

The rectifier I 58 is illustrative of connection to one leg I8I of a delta-star connected three phase transformer. The secondary of the leg I8I has a rectifier tube I82 and the motor armature I54 serially connected across it. The rectifier tube I82 has a plate I83, a control grid I84 and a cathode I85. The output of the rectifier tube I82 is supplied to the motor armature I 54 by the aforementioned series connection. The output of the phase shifter I55 is supplied through an output transformer I to the grid I84 with respect to the cathode I85 of the rectifier tube I82. The star point, illustrated at one end of the secondary of the transformer leg I8I, would be the star point or common point of the secondary of the three phase transformer, if a three phase rectifier system were used.

The controlled voltage source I62 includes a shunt resistance I86 connected across the motor armature I54. The shunt resistance I86 has a tap connection I81 for supplying a direct current feedback voltage to the phase shifter I 55 through a movable contact I88 on the voltage divider I18. The direct current feedback voltage obtained from the shunt resistance I86 supplies a negative controlled voltage to the grid I 16 of the tube I1I. whereas the voltage divider I18 supplies either a negative or a positive controlling voltage to control th'eamount oi bias applied to the tube Ill. The amount of bias supplied to the tube HI determines the effective reactance of this tube, and consequently the operating position of the out put terminal P on the arcuate'locus of the voltage vector diagram. The operation ofthe circuit of Figure 13 is substantially the sameas for the circuit of Figure 12, and therefore will not be repeated.

The circuit of Figure 14 shows another form of energy conversion system using a phase shifter 28!! which is of the form of phase shifter as shown in the Figure 3. The energy conversion system of Figure 14 includes, besides the phase shifter 28!], a controllable rectifier 2m supplying recti fed energy to a direct current motor armature 202. The phase shifter 220 includes an energi"'- ing transformer 203 having the primary thereof connected to an alternating current source 204 and having a secondary 265 with a center tap 206. seriall connected across the secondary 285 are a resistance 28! and a condenser 208. The voltage across the resistance 2G1 establishes the baseline voltage and connected across this resistance are a condenser 208 and a variable inductance 2H1. The variable inductance 2 i D has been shown as a rectangle with a symbol for an inductance shown dotted therein. The first output terminal is connected at the center tap 22:8 and the second output terminal P is connected at the junction of the condenser 20!! and inductance 2 i 0. The output of the phase shifter 209 therefore appears across the terminals 0 and P and is supplied to first'and second impedances 2! l and 212, respectively.

The controllable rectifier 20! is shown as a full wave rectifier including the push-pull connected rectifier tubes 2 l 3 and 2 M. The output from the phase shifter 2&0 is applied to the grids and cathodes of these rectifier tubes 213 and 2M in push-pull in a well-known manner to control the output of the rectifier 2!" from maximum output down to a minimum which may be zero output. The output of the rectifier 2!]! appears at the first and second output terminals 2l5 and 216 and is applied across the motor armature 202'. A field winding 21'! is provided for the motor armature 202 and is energized from a direct current some 218. Also energized from the direct current source 218 is the series combination of a voltage dropping resistance M9 and a voltage'regulator tube 220. Connected in parallel with the voltage regulator tube 220 is a voltage divider 22! having a movable tap 222. A'lead 223 connects the movable tap 222 to a control terminal 224 on the variable inductance 2l0, and a lead 225 connects the positive end of the motor armature 202 to a second control terminal 226 on the variable inductance 2H).

The operation of the motor control system of Figure 1 is in general similar to the operation of the motor control circuits of Figures 10, 12 and 13, since there is a phase shifter controlling a controllable rectifier supply variable energization to a direct current motor armature. The phase shifter 209 is a form of the phase shifter shown in Figure 3 wherein the branch circuit 32 has been shown specifically as a transformer secondary having a tap thereon. The vector diagram for the phase shifter 200 will be similar to the vector diagram of Figure 4, wherein the vectors E30 and E31 are collinear and preferably equal. Since the tap 29B of this secondary 205 has been shown as a center tap it would be advantageous to have the locus 29 of the output ter-- inal P large enough so that the alternating current input voltage vector is substantially a diameter thereof. This would establish the point 0' near the center of this circular are 29. The are 29 will be a circle if the Q of the inductance 2 it remains constant while its impedance is varied. This may readily be accomplished by making the variable inductance a reactance tube was done in the Figures l0, l2 and 13, or it may also be accomplished in other ways by using other forms of variable inductances, such a saturable re-' actor.

It will be noted that the controlling voltage obtained at the movable tap 222 and the controlled voltage across the armature 202 are unidirectional voltages which are combined in opposition and applied to the control terminals 224 and 226. The controlled voltage from the armature 202 may be considered as a voltage feedback arrangement which may be used in conjunction with the controlling voltage from tap 222 for giving a signal usable to maintain the speed of the motor armature 292 substantially constant. Thus, this voltage may be termed as a control signal voltage. The voltage from the movable tap 222 may be considered as a controlling voltage for controlling the amount of impedance of the variable inductance 210, which in turn will affect the phase of the output voltage from the phase shifter 200 and hence control the speed of the motor armature 202. Thus, the voltage from the voltage divider 22! may be considered as a speed controlling voltage.

The circuit of Figure 15 shows modification which may be substituted for a portion of the motor control circuit of Figure 14. The circuit of Figure 15 is a generator field control circuit including a generator armature 238 and a generator field 23!. In this case the generator field 231 is that which is connected to the output terminals 2|5 and M6 of the controllable rectifier 20!, not shown in this Figure 15. Other circuit elements duplicated in this Figure 15 are the direct current source 2 I8, the controlling voltage divider 22| and associated voltage regulator tube 220-, and the variable inductance 2 HJ. Connected across the generator field 231 is a feedback resistance 232 having a tap 233. This tap 233 is connected by the lead 225 to the control terminal 226 of the variable inductance 2H1. The controlling voltage divider 22! again has movable tap 222 connected by the lead 223 to the control terminal 224 of the variable inductance 2 l 0. The generator armature 230 is connected in loop circuit with a motor armature 234 having a field winding 235 energized from the direct current source 218. The generator armature 230 is driven from any suitable prime mover 236.

The operation of the modified circuit of Figure 15 is essentially the same as that for the motor armature control circuit of Figure 14.. The output of the controllable rectifier at the terminals 2 l5 and 2|6 is applied to the generator field 23! rather than to a motor armature; however, this variation in field energization will control the speed of the motor armature 234 in a well-known manner. The feedback of controlled voltage to the variable inductance 2!!! is a feedback of only a part of the voltage appearing across the genera.- tor field 23!, rather than being a feedback of the entire rectifier output voltage. The voltage appearing at the control terminals 224 and 226 is again a control signal voltage which is used in some manner to control the impedance of the variable inductance 2H).

The circuits of Figures I l and each have a safety feature inherent in the circuit arrangement. This safety feature is found in the choice of phase shifter 280 for use with this motor arma ture or generator field. control system. The vector diagram of Figure l shows generally the vectors obtainable from the phase shifter 256 with the vector E27 of this vector diagram being that which would signify the voltage vector of the variable inductance 2H3. Further the vector E25 would be that which would signify the vector of the corn denser 269. Thus, if the variable inductanc 2E0 should fail for any reason, namely, have an open circuit therein, or if the condenser 298 should have a short circuit, the voltage across the variable inductance 210 relative to the voltage across the condenser it!) would be infinite, and thus the point P would rotate in a cloclnvise direction to a point at or near the point 23 of this voltage vector diagram. At this point it will be observed that the output voltage vector Em will be approximately 1.80 degrees lagging the vector of the input voltage. This 180 degrees lagging rela tionship of the output of the phase shifter will establish the output of the rectifier am at a mini mum to thus slow the speed of the motor armature 2% or 23s to a minimum and hence safe value.

The circuit of Figure 16 is a controllable energy conversion system which includes a phase shifter a controllable rectifier Edi a field Wind'- ing M2 or a direct current motor '1; direct current motor 2% also has an armature M l energized from a separate direct current source indi cated at 245. The phase shifter 248 is energized through a transformer 2853 from an alternating current source 2M and the transformer Ell-ii has a secondary 205 with a center tap 2% which is also the first output terminal 0 of this phase shifter N53. The phase shifter 2M3 also includes the resistance iltll and condenser 26% Serially con nected across the resistance 2H is a serially connccted variable capacitance 2 36 and an inductance 26?. The variable capacitance 246 includes a thermionic tube 248 having a plate 24? a screen grid Elli), a control grid 25S and a cathode 252. A condenser 253 is connected between the plate 249 and. the control grid and a resistor 2M and condenser 255 interconnect the control grid Eli! and. cathode The condenser 253 and resistor 254 establish that the voltage applied to the control grid. 25! is approximatel 90 degrees leading the voltage applied tothc plate N9, both voltages being relative to the cathode 252. This 90 degrees leading grid voltage establishes that the thermionic tube 2&8 acts as a capacitance which is variable in accordance with the variations in. bias Voltage. A. direct current source 2 it supplies through. voltage drop-ping res "or it?! a voltage to the controlling voltage divider 22! which has a movable tap 222. Connected across the voltage divider Elli is a voltage regulator tube 228 with the cathode of this voltage regulator tube connected to the cathode 252 and the anode of this voltage regulator tube connected to the screen grid 256 of th thermionic tube 2 M The second output terminal. P of the phase shifter 2st is connected to the junction between inductance M! and the voltage regulator tube 228 which for alternating current purposes, is the junction of the inductance M? and the variable capacitance 245. The output of the phase shifter 2 in, from the output terminals 0 and P, is supplied to agrid transformer which in turn applies the phase shiftabl'e output voltage to the controllable rectifier 2M which ls'shown as a full wave recti her. This rectifier is also supplied from the alter nating current source 284 through the power transformer 25?. The output of the controllable rectifier 24! appears across the output terminals 258 and 259 and is thus applied across the motor field 2 32. Connected in parallel with the motor field 242 is a feedback resistor 2% having a tap 251. Th tap 26! is connected by a lead 252 through the filter resistors 2G3 and 264 to the junction 265 of the resistor and condenser 255. A filter condenser 2553 interconnects the junction of the resistors 2E3 and 264 to the oatheds 252.

In operation, the motor field control energize.- tion circuit of Figure 1'5 utilizes a phase shifter 249 which is similar to that shown in Figure 3. The variable capacitance 245 and the inductance 247 have the second cu out terminal P connected therebetween, and hen by varying the effective bias on the thermionic tube 268 the locus of the potential of this second output terminal P will vary on an are which may approximate a circular arc since the variable capacitance 246 is a reactance tube. The bias on the reactanoe tube 243 is applied across the control grid 25! and cathode 252 which in effect is the voltage applied across the condenser 25 5. This bias voltage is a combination of a positive controlling voltage derived across the right-hand portion of the controlling voltage divider 22! and a negative controlled voltage derived from the left-hand end of the feedback. resistor 26s. The filter resistors 263 and 264 and the filter condenser 266 reduce the alternat ing current ripple from this feedback voltage in order to present substantially constant direct current biasing voltage to the thermionic tube 2548. In this circuit of Figure 16 the variable element of the phase shifter 2 51) has been shown as a variable capacitance as a safety feature for this motor field energization circuit. In the event of failure of the thermionic reactance tube 2% the voltage drop thereacross will be very high compared to the voltage drop across the inductance 2t? and hence the point P on the voltage vector diagram of Figure 4 will rotate in a counterclockwis direction to a point which is approximately degrees leading relative to the alternating current input voltage, with which the anode voltage is in phase.

'Since the phase of the voltage on the two grids is 120 degrees leading relative to the respective anode voltages of the controllable rectifier 265, the rectifier 24! will have a full output to thus supply full field energization to the motor field 242. This will establish the speed of the motor armature 24 t at a minimum value which will be a safe condition in the event of failure of the thermionic reactance tube 248.

The movable tap 222 is a speed control since it controls the amount of controlling voltand the feedback voltage from the feedback resistor 25!! is again. controlled voltage which together with the controlling voltage gives a control. signal or bias voltage tending to maintain the unidirectional voltage across the field Winding M2 at a constant value, irrespective of fiuctuations in the voltage of the alternating current source 25%.

Although the invention has been described in its preferred form with a certain degree of particularitv, it understood that the present disclosure of the preferred form has been made only by Way of example and that numerous changes in the details of circuit construction and the combination and arrangement of circuit elements may be resorted to without departing from the spirit and the scope of the invention here inafter claimed.

What is claimed is:

1. An electrical control system for an electrical converter connected to an alternating current source and having control means for varying its power output to an electrical load comprising, a phase shifting network having a phase shiftable output voltage between first and second. output terminals, means for connecting said first and second output terminals to said control means of said converter, two series-connected relatively variable reactive elements of opposite sign, means for energizing said serially connected elements from a reference voltage derived from said alternating current source, said first output terminal being at the junction of said elements so that as the impedances of said elements are varied rela tively to one another, the locus of the potential of the first output terminal lies, in a vector diagram, on an arc spanning the reference voltage vector, means for establishing said reference voltage at a phase angle relative to said alternating current source that if the relative impedance ratio of said elements tends toward infinity in a given sense the output voltage vector tends to become parallel to the vector of a voltage of said alternating current source, circuit elements energized from said alternating current source, and means for connecting said second output terminal to said circuit elements so that the potential of said second output terminal lies, in the vector diagram, within the space bounded by the reference voltage vector and said arc.

2. An electrical control system as claimed in claim 1, in which the arc spanning the reference voltage vector subtends at the second output terminal an angle substantially greater than 180 degree 3. An electrical control system as claimed in claim 1, in which at least one of the reactive elements comprises a thermionic tube provided with a quadrature feedback circuit so that it acts as a reactive element.

4. An electrical control system as claimed in claim 3, in which the thermionic reactance tube has a control electrode and the efiective impedance of such reactive element is varied by regulating the bias voltage applied to said electrode.

5. An electrical control system as claimed in claim 4, in which a voltage from the quadrature feedback circuit and the variable bias voltage are applied to the same control electrode of the tube.

6. An electrical control system for an electrical converter connected to an alternating current source and having control means for varying its power output to an electrical load, comprising, a phase shifting network having a phase shiftable output voltage between first and second output terminals, means for connecting said first and second output terminals to said control means of said converter, two series-connected relatively variable reactive elements of opposite sign, means for energizing said serially connected elements from a reference voltage derived from said alternating current source, said first output terminal being at the junction of said elements so that as the impedances of said elements are varied relatively to one another, the locus of the potential of the first output terminal lies, in a vector diagram, on an arc spanning the reference voltage vector, means for establishing said reference voltage at a phase angle relative to said alternating current source that if the relative impedance ratio of said elements tends toward infinity in a given sense the output voltage vector tends to become parallel to the vector of a voltage of said alternating current source, circuit elements energized from said alternating current source, means for connecting said second output terminal to said circuit elements so that the potential of said second output terminal lies, in the vector dia gram, within the space bounded by the reference voltage vector and said arc, means for developing a controlled voltage proportional to the voltage applied to said load, means for developing acontrolling voltage, means for balancing said controlled voltage against said controlling voltage to establish a resultant voltage, and means for controlling the relative impedance of said reactive elements by said resultant voltage to maintain the voltage across the load substantially stable at a value determined by the controlling voltage.

7. An electrical control system as claimed in claim 1, in which the reference voltage for the phase shifting network is derived across one of first and second impedances connected at least partly in series and energized from the alternating current source, one of said impedances being reactive so that the voltages across them are substantially in quadrature, and the two series-connected reactive elements being connected across one of said impedances.

8. An electrical control system as claimed in claim 7, in which one of said output terminals is common with a terminal of said alternating current source.

9. An electrical control system as claimed in claim 1, in which the reference voltage for the phase shifting network is derived across one of first and second impedances connected at least partly in series and energized from the alternating current source, one of said impedances being reactive so that the voltages across them are substantially in quadrature, and the two series-connected reactive elements being connected acrosl one of said impedances, said circuit elements in cluding third and fourth impedance means con nected in series and energized by the alternating current source and having the second output ter minal in the connection between them.

10. An electrical control system as claimed in claim 9, in which the third and fourth impedance means are such that the voltages across them have substantially the same phase angle.

11. An electrical control system as claimed in claim 1, in which the reference voltage for the network is derived from a first impedance energized from the alternating current source, the arrangement being such that the reference voltage is substantially in phase with but is less than the voltage across said first impedance.

12. An electrical control system as claimed in claim 11, in which the two series-connected reactive elements are connected to tapping points on the first impedance, second and third seriesconnected impedances connected across the first impedance, at least one of said second and third impedances being reactive, the second output terminal being in the connection between the second and third impedances.

13. An electrical control system as claimed in claim 1, in which said two series-connected reactive elements are connected in parallel with a circuit consisting of two series-connected reactive arms of opposite sign and having the second output terminal in the connection between them, the arrangement being such that the phase angle between the voltages across said arms is approximately twice the phase angle between the voltages across said elements.

14. An electrical control system as claimed in claim 1, in which the circuit elements are serially connected reactive arms of opposite sign having the second output terminal therebetween, means for energizing said reactive arms from said alternating current source, the product of the circuit Q and the energizing voltage for the reactive elements being substantially twice as great as the same product for the reactive arms.

15. An electrical control system as claimed in claim 1, in which the alternating current source is a polyphase source and the phase shifting network is supplied from a phase of the source other than the phase supplying said controllable converter.

16. An electrical control system as claimed in claim 1 for the speed control of a direct current 20 motor supplied from the converter output, said alternating current source being three phase, said converter including a space discharge device having a control electrode and an anode,

the inductive reactance of the series-connected 25 reactive elements being a reactance tube, said reference voltage of the network being derived from a phase of the source which lags by 120 degrees with respect to the phase supplying the converter space discharge device controlled by such network whereby in event of failure of the reactance tube, the voltage supplied to the control electrode of the discharge device is approximately degrees out of phase with its anode voltage and the supply to the motor from the discharge device is cut oil.

17. An electrical control system as claimed in claim 1 for the speed control of a direct current motor supplied from the converter output, said alternating current source being single phase, said converter having an anode and a control electrode, the inductive reactance of the seriesconnected reactive elements being a reactance tube, and a transformer connected to one of said anode and control electrode in the appropriate sense so that in event of failure of the reactance tube the voltage supplied to the converter control electrode is approximately 180 degrees out of phase with the corresponding anode voltage whereby the supply to the motor from the converter is cut off.

WALTER. J. BROWN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,719,866 Alexanderson July 9, 1929 1,851,692 Zucker Mar. 29, 1932 1,894,114 Mittag Jan. 10, 1933 1,986,622 Case Jan. 1, 1935 2,194,357 Green Mar. 19, 1940 2,537,767 Langenwalter Jan. 9, 1951 

